This invention relates to a cyclonic separation device and in particularly but not solely to a cyclonic separation device for a vacuum cleaner.
Cyclonic separation devices are widely used in vacuum cleaners to separate dirt and dust from the airflow. Typically such vacuum cleaners incorporate a single upstream cyclone separator which is relatively large in diameter and which is suited to separating heavy dirt and dust particles as well as coarse and fibrous matter from the airflow.
Generally, a cylindrical shroud is mounted concentrically inside the cyclone chamber of the upstream stage such that air in the cyclone chamber rotates around the shroud and is drawn radially inwardly into the interior of the shroud through apertures which are formed in the side wall thereof. The shroud partially acts as a filter to prevent large lighter matter leaving the cyclone chamber and also acts to shape and constrain the airflow in the cyclone chamber.
A problem with such shrouds is that the apertures therein can become blocked with dirt and dust.
GB2397785 discloses a cyclonic separation device in which the partially cleaned air leaves the cyclone chamber through a rotatable shroud disposed axially within the cyclone chamber. The shroud comprises axially extending louvers which act as vanes that cause the shroud to be rotated by the induced airflow in the cyclone chamber. The document alleges that an advantage of this arrangement is that the rotary motion of the shroud dislodges any dust on the shroud by centrifugal action. A problem with this arrangement is that the speed of the shroud substantially lags behind the speed of the airflow and does not reach a significant enough speed to dislodge the dust thereon. In fact, the shroud actually acts to slow the air thereby causing a pressure drop and a loss of efficiency.
GB2389064 discloses a cyclonic separation device in which the partially cleaned air leaves the cyclone chamber through a rotatable shroud disposed axially within the cyclone chamber. The shroud is rotated at a low speed by a motor and gear train to cause the external surface of the shroud to be wiped of dust by a static brush.
Another problem with shrouds is that the rotational airflow inside the cyclone chamber of the first stage has to decelerate and turn radially inwardly to pass through the apertures, thereby causing a pressure drop and a loss of suction.
We have now devised an improved cyclone separation device.